1. Field of the Invention
The present invention relates to a method and apparatus for handling re-establishment of a radio link control entity in a wireless communications system, and more particularly, to a method and apparatus for timely polling status of a peer radio link control entity, and preventing waste of system resource.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates.
The Access Stratum (AS) of the 3G mobile communications system comprises various protocol stacks, such as Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). In addition, the 3G mobile communications system also provides different levels of transmission quality, and can operate in different modes according to different transmission quality requirements, such as Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). TM is appropriate for use in services with high requirements for real-time transmission, UM is appropriate for use in services with requirements for real-time transmission and packet sequencing, and AM is appropriate for use in services with low requirements for real-time transmission, but high requirements for data accuracy.
In AM, the RLC layer is a combination of a transmitting side and a receiving side. The transmitting side and the receiving side each process transmission and reception in the RLC layer, and both sides can share system resources. In some circumstances, the RLC layer must be re-established, e.g. when starting a re-establishment procedure. The prior art re-establishes the RLC layer by re-establishing the transmitting side or the receiving side.
Directed at operations corresponding to re-establishing the RLC layer, the related communications protocol specification discloses that if only the receiving side is re-established, the prior art will discard all control PDUs (Protocol Data Unit) except MRW SUFI (Move Receiving Window Super Field). In other words, a POLL SUFI (Poll Super Field) will be discarded. The POLL SUFI is utilized for polling status of the peer RLC entity. Therefore, when only the receiving side is re-established, the prior art cannot timely request a status report from the peer RLC entity.
Similarly, the related communications protocol specification further discloses that if only the transmitting side of the RLC entity is re-established, the prior art will discard MRW SUFI, RESET PDU, and RESET ACK PDU. In other words, the POLL SUFI will not be discard in this case, causing transmission of an unnecessary STATUS PDU or piggybacked STATUS PDU and waste of system resource.